Is There a Relationship Between Smoking and Asthma in Adults?

Transcription

1 The Journal of International Medical Research 1999; 27: Is There a Relationship Between Smoking and Asthma in Adults? LBEN-NoUN Department of Family Medicine, Faculty of Health Sciences, Ben-Gurian University of the Negev, Israel A case-control study was carried out to investigate the possibility ofa relationship between smoking and asthma in adults. The study group of 141 asthmatic adults and 423 age- and sex-matched non-asthmatic controls were selected from 4341 men and women aged 18 years and over, who were registered with a family practice. Both groups were interviewed by telephone about past and present smoking habits. Current smokers constituted 22% of the asthmatic group and 15% of the controls (not significantly different). The prevalence ofthose who had given up smoking (quitters) was significantly higher in asthmatics than in controls (8.5% versus 3.6%). Asthma began at younger ages in smokers than in quitters and non-smokers. In smokers, the duration of smoking was associated with the duration of asthma. No other significant differences in or associations between smoking habits and asthma were found. No major relationship between smoking and asthma was demonstrated. KEY WORDS: SMOKING; ASTHMA; ADULTS 15

2 INTRODUCTION Bronchial asthma is a common chronic disease of the airways of both children and adults. Identification of environmental influences on asthma is important as an aid to asthma prevention and more effective treatment. The possibility of a relationship between smoking and asthma has been the subject of controversy. It has been reported that atopy and active cigarette smoking are associated with the incidence and recurrence of wheezing during adulthood,' and that smoking is a risk factor for asthma.p On the other hand, asthma prevalence and incidence have also been reported to be independent of cigarette smoking! Other workers showed that women who were current smokers had a significantly lower risk of asthma than women who had never smoked and women who had given up smoking." Thus, it may be that smoking is not a strong risk factor for asthma.y This study was conducted to determine whether any association exists between smoking and asthma in adults. The present study is part of a comprehensive adult asthma research programme conducted at three family practices from which data on the prevalence of asthma in adults have been published previously. B PATIENTS AND METHODS PATIENTS AND CONTROLS The study was carried out in three urban family practices in southern Israel, with a total population of 4341 patients, aged 18 years and older. In June 1996, the medical records of all subjects were systematically reviewed and information was extracted from 144 files in which the physicians recorded diagnoses of active asthma during the previous year. A history of wheezing was considered the diagnostic criterion for physician-diagnosed asthma in this study, an approach that is widely accepted.'l -!2 Other criteria used were as described by Gellert et a1.!2 with slight modifications. Patients were considered to have asthma if (1) a diagnosis of asthma had ever been made in general practice or in hospital, whatever the presenting symptoms, (2) bronchodilator therapy had ever been administered for wheezing or bronchospasm, or (3) wheezing or bronchospasm had ever been noted in the medical records on more than one occasion, even if bronchodilator therapy was not given. The diagnosis of chronic bronchitis was based on a history of cough with productive sputum for at least 3 months per year, for the previous 2 consecutive years. J:j A control group was selected from the same practice list and included nonasthmatic subjects aged 18 years and older. The files of the control group were extracted in alphabetical order; for each asthmatic patient, three non-asthmatic controls, matched for age and sex, were included. STUDY CONDUCT Each subject was interviewed by telephone, to obtain data on asthma and smoking histories. Subjects were asked 'Has a doctor ever told you that you have asthma? When did your asthma begin? Do you still have asthma?' Other questions included the age of starting to smoke, the average number of cigarettes smoked per day in active smokers (and just before quitting in those who had stopped), and age of quitting. As a result of the interviews three patients were excluded form the list because the diagnosis of asthma was questionable. Only a single record of asthma, recorded 10 years previously, was found in each of these patients' files. These patients also denied having an asthma attack 16

3 during the preceding 10 years. A regular smoker was defined as someone who smoked more than one cigarette per day for at least a year. A quitter was defined as someone who had given up smoking for at least a year before the interview; those who had given up smoking more recently were considered current smokers." STATISTICAL ANALYSIS Data were analysed using the Statistical Package for the Social Sciences (SPSS). Continuous variables were compared using Student's r-test. Grouped data were compared by the Mann-Whitney U test and Pearson correlation test. A multivariate logistic regression model was used to assess the relationship between various smokingrelated variables and asthma. A significant difference was defined as P < RESULTS The asthma group consisted of 141 patients, of whom 64 (45.4%) were men. The control group comprised 423 non-asthmatic subjects, of whom 192 (45.4%) were men. Table 1 demonstrates that the prevalence of current smoking did not differ significantly between asthmatics (22 %) and controls (15.1 %). The prevalence of quitters was significantly higher in asthmatics than in controls (8.5% versus 3.6%; P < 0.03). The proportion of non-smokers was significantly higher in controls than asthmatics (81.3% versus 69.5%; P < 0.002). In both asthmatic patients and controls, smokers were younger than quitters and non-smokers. No significant difference was found in smoking habits between asthmatic and control group smokers, or between asthmatic and control group quitters (no significant difference between asthmatics and controls, in either smoking group; P < 0.02 for asthmatic smokers versus asthmatic quitters, and P < for control smokers versus control quitters). There was no significant difference in the duration of asthma between asthmatic smokers and quitters, and those who had never smoked. Asthma began at a significantly younger age in smokers than in quitters and non-smokers (P < 0.03). Table 2 shows that, of the various smokingrelated variables examined in asthmatic patients, only duration of smoking was significantly associated with duration of asthma in current smokers (P < 0.001). DISCUSSION Asthma in adults is frequently encountered in family practice." The current prevalence of physician-diagnosed asthma in adults, the relationship between asthma and sociodemographic characteristics, the pattern of medication use by asthma patients and the characteristics of the comorbidity in asthma in adults have all been considered in an earlier publication." There are conflicting reports concerning the relationship between smoking and asthma; further evaluation of this possible relationship was undertaken to increase our understanding of the factors involved in the development of asthma in adults. A variety of methods have been used to define asthma:" subject reports of doctor diagnosis, self-diagnosis, symptoms, record review, or examinations (sometimes including pulmonary function or laboratory tests). Each method will identify a somewhat different population of asthmatics, and the results are not directly comparable. Because asthma is an episodic condition, pulmonary functions vary over time. Pulmonary function testing under challengeby a bronchospastic agent can identify a group with reactive airways, and can be positive even in former asthmatics." Thus, in this study, adult asthma diagnosis was based on record review, doctors' diagnoses, and patients' reports of doctors' diagnoses. 17

4 Selected characteristics ofadult asthmatics (n = 141) in comparison with an age and sex-matched control group (n = 423) Smokers Quitters Non-smokers Asthmatics Controls Asthmatics Controls Asthmatics Controls (n =31) (n =64) (n =12) (n =15) (n =98) (n =344) Age (years )a 43.6 (16.2) 47.1 (14.5) 68.8 (12.6) 70.5 (10.5) 54.9 (17.6) 53.6 (17.6) Age when asthma beqan'' 27.9 (13.7) 37.6 (16.8) 37.3 (18.8) Duration of asthma" 15.1 (13.2) 26.3 (20.0) 17.1 (13.9) Age of starting to smoked 21.3 (7.8) 18.6 (5.6) 19.3 (10.7) 18.7 (4.7) "-\ ee Duration of smoking" 22.5 (18.0) 28.9 (15.7) 32.3 (15.1) 35.8 (17.0) No. of cigarettes smoked per day' 14.6 (6.2) 17.5(9.7) 35.9 (12.8) 27.5 (14.9) Values are means only (SDs). "P < for asthmatic smokers versus asthmatic quitters and asthmatic non-smokers; P < for control smokers versus control quitters and control non-smokers. Not significant for asthmatics versus controls, in all three smoking categories. bp < 0.03 for asthmatic smokers versus asthmatic quitters and asthmatic non-smokers. 'Not significant for asthmatic smokers versus asthmatic quitters and asthmatic non-smokers. dnot significant for asthmatics versus controls, in either smoking group, nor for smokers versus quitters, in either asthma group. "Not significant for asthmatics versus controls, in either smoking group, nor for smokers versus quitters, in either asthma group. fnot significant for asthmatics versus controls, in either smoking group; P < 0.02 for asthmatic smokers versus asthmatic quitters, and P < for control smokers versus control quitters.

5 TABLE 2 Relationship between smoking habits and asthma among smokers and quitters: regression coefficients and their statistical significance Smokers Quitters Regression Regression coefficient P-value coefficient P-value Age of starting to smoke versus age when asthma began Duration of smoking versus duration of asthma No. of cigarettes smoked per day versus age when asthma began No. of cigarettes smoked per day versus duration of asthma Years without smoking versus age when asthma began Years without smoking versus duration of asthma Years without smoking versus no. of cigarettes smoked per day The strength of agreement between patient reports and patient medical record information is substantial (IC < 0.6) for asthma." The validity and reliability of physicians' claim data for epidemiological study have been confirmed in previous reports.v'-" Furthermore, patient reports of a physician's diagnosis of asthma appears to be as valid and reliable as any other measure of this condition. 6,15,21,22 The prevalence of current smoking among asthmatics was 22% compared with 15.1% in non-asthmatics, but this difference was not statistically significant. Moreover, the smoking habits of current smokers did not differ significantly between asthmatic and control group current smokers. In previous reports, widely differing figures for smoking prevalence have been reported including 6.94%23 and 15.4%24 of adult asthma patients, 50.3% of male and 22.4% offemale adult asthma patients;" in another study 60% of asthma patients aged 10 to 39 years, and 45.5% aged 40 years and older were current smokers," and in a further report, 64.7% were ever smokers." Non-smokers constituted the largest group of subjects studied, with significantly more control subjects than asthmatic patients, while quitters were the smallest group with significantly more asthmatic patients than controls. Quitters were older than either smokers or non-smokers both in asthmatic and control groups. Furthermore, quitters in these two groups had smoked significantly more cigarettes per day (before they had stopped smoking) than current smokers now smoked. The age and number of 19

6 cigarettes smoked per day just before quitting did not significantly differ between asthmatic and control group quitters. The higher prevalence of quitting in asthmatic patients indicates that asthmatics had stopped smoking more often than control subjects, probably because of the development of severe asthma symptoms. Asthma began at a younger age in smokers than quitters and non-smokers. Nevertheless, the age of onset of asthma was not significantly associated with smoking in either current smokers or quitters. Among other smoking variables examined among currently asthmatic smokers and quitters, only the duration of smoking was associated with the duration of asthma among smokers. Other factors related to asthma, such as atopy, passive smoking, carpets and rugs, or keeping cats and dogs, were not evaluated since the objective of the study was to examine the relationship between current and former smoking habits and asthma. The practices that participated in this study are run by specialist family physicians and there is a professional difference between them and non-specialist general practitioners. In addition, the diagnosis of asthma could be affected by a diagnostic bias towards labelling some patients as having chronic bronchitis rather than asthma. Such factors, however, inevitably influence any study ofthis kind and the present study was considered to be the optimal approach to collecting data about smoking habits in the family practice over a 1-year period. In summary, although some factors interacted with asthma, no significant association between asthma and smoking could be demonstrated. These results add to our understanding of some of the characteristics of asthma in adults. ACKNOWLEDGEMENTS I am pleased to acknowledge the statistical assistance I received from Mrs Nava Yelin and Erez Batat form the Statistical Department of Kupat Holim. REFERENCES 1 Strachan DP, Bultand BK, Anderson HR: Incidence and prognosis of asthma and wheezing illness from early childhood to age 33 in a national British cohort. BMJ 1996; 312: Larsson L: Incidence of asthma in Swedish teenagers: relation to sex and smoking habits. Thorax 1995; 50: Flodin D, Jonsson P, Zieger J, et 01: An epidemiological study of bronchial asthma and smoking. Epidemiology 1995; 5: McWhorter WP, Polis M, Kaslow RA: Occurrence, predictors, and consequences of adult asthma in NHANESI and follow-up survey. Am Rev Resp Dis 1989: 139: Troisi T, Speizer FE, Rosner B, et 01: Cigarette smoking and incidence of chronic bronchitis and asthma in women. Chest 1995; 108: Vesterinen E, Kaprio J, Koskenvuo M. Prospective study of asthma in relation to smoking habits among adults. Thorax 1988; 43: Schachter E, Doyle CA, Beck GJ: A prospective study of asthma in a rural community. Chest 1984; 85: Ben-Noun L: Characteristics of asthma among Israeli adults. 1STJMed Sci 1997; 33:

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